The present invention relates to systems for the thermal processing of commodities, such as foodstuffs or pharmaceutical products. The invention particularly involves the thermal processing of such items packed in containers formed of material that is light in weight and/or of reduced wall thickness wherein the process can be conducted on a continuous basis and in which cooling is effected in a hydrostatic water column.
It is well known that the amount of labor required for implementing thermal processing of commodities in an effectively controlled manner can be reduced through the use of continuously operated, high capacity sterilizers (termed "cookers" herein) having a hydrostatic cooling tower positioned downstream and through each of which, containers being processed are conducted via a continuous conveyor. However, notwithstanding their desirability, systems of this type have heretofore had limited application, essentially to only products packed in containers, such as glass or metal containers having sufficient container wall strength in order to withstand the maximum external pressures imposed by the system. In these systems, the containers are conducted through a multitude of sterilization and cooling towers or legs in which pressure control is provided by air overpressure. As a result of such measures, the containers are caused to experience stepped pressure changes in travelling through the respective cooling towers or legs whereby the containers are subjected to a plurality of levels of essentially constant pressure.
Experience has shown that light-weight containers, as for example those catagorized as "thin-walled" or "semi-rigid" plastic containers are unsuitable for processing in thermal systems of the described type due to the fact that such containers are highly deformable and normally require overpressure during cooking and pressure control during cooling in order to compensate for lack of container strength and the inability to withstand significant internal and external pressure differentials during processing. In the processing of such containers a more gradual pressure ramp is required that heretofore has only been achievable in batch retorts which preclude the processing of containers on a continuous basis.
It is to the amelioration of this problem, therefore, to which the present invention is directed.